← Encyclopedia of Astrology · lesson 109/235
Aspect strength
The idea
Of everything that might make one aspect "stronger" than another, the one point nearly every school agrees on is closeness. Lilly distinguished a partile aspect, exact to the degree, from a platic one, within the orb but not exact; Isabel Hickey compared a near-exact aspect to sitting right on the stove, where a wider one is felt only as warmth. A tight aspect is generally read as louder and more constant; a wide one as quieter.
But "3° wide" does not mean the same thing for every pair. Three degrees is comfortably inside the allowance for a Sun–Moon trine and outside it altogether for an aspect to a small asteroid. So the useful measure is not the orb alone, but the orb against the allowance for that particular aspect and pair.
How it is worked out here
Strength = 1 − orb ÷ allowance.
It runs from 1, when the aspect is exact, down to 0 at the very edge of what is allowed. The allowance is the one described under orb: each body carries one (8° for the Sun and Moon, 7° for the Ascendant and Midheaven, 6° for the other planets and the nodes, 2.5° for asteroids and minor points), a pair takes the tighter of its two, and the minor aspects are capped further (2° for the semi-square and sesquiquadrate, 1.5° for the quintile and biquintile).
Some examples:
| Aspect | Orb | Allowance | Strength |
|---|---|---|---|
| Sun trine Moon | 3° | 8° | 0.63 |
| Mars square Saturn | 2° | 6° | 0.67 |
| Venus semi-square Jupiter | 1° | 2° | 0.50 |
| Moon opposite Mercury | 0°30′ | 6° | 0.92 |
The Sun–Moon trine and the Mars–Saturn square have different orbs but similar strength, because each is judged against its own limit. Parallels and contraparallels are measured the same way against their 1° allowance of declination: a parallel 0.3° from exact has a strength of 0.7.
What it does not include
Strength is deliberately one thing only. It does not fold in:
- whether the aspect is applying or separating — that is shown beside it, because a tight separating aspect and a wide applying one both have something to say;
- which planets are involved — a tight aspect between two slow outer planets is shared by everyone born for months either side;
- whether the aspect is hard or soft — a strong square is a strong square.
Reading an aspect still means weighing all of these together. Strength only answers the question how close? in a way that can be compared from one aspect to the next.
How it is shown here
The Aspects and Parallels tables have a Strength column. Depending on how scores are set to display, it appears as the number itself, an L / M / H label, or a 1–10 scale — the labels and scales relative to the other aspects in the same list. It is for information only: the tables are still ordered by orb, and nothing in a reading is chosen by strength. Charts made before the allowance was stored with each aspect show no strength at all rather than a guess.
Aspect patterns carry a strength of the same kind: how tight the figure's loosest leg is against the 10° the detector allows.